1. Field of the Invention
The present invention relates to an obstetric vacuum extractor of the type which has a vessel that has an evacuable vessel chamber open to one side and on which a pulling device is fastened.
2. Description of the Prior Art
Vacuum extraction has been approved for surgical vaginal obstetrics for years. Known devices employed to this end (such as the vacuum extractor known for example from U.S. Pat. No. 2,702,038) consist of an evacuable vessel, the opening of which is applied to the infant's head after introduction into the vagina of a parturient. As a vacuum is created in the vessel, the head adheres to the vessel by suction, with formation of a tissue swelling, so that then through a holding handle and controlled pull movements the birth process can be supported and also accelerated.
However, vacuum extraction, like other instrument delivery aids, are not without risk. At too strong a pull and in particular upon the occurrence of traction forces extending tangentially to the vesel, the vessel adhering to the head of an infant by suction may unintentionally and abruptly detach from the scalp, and this may lead to considerable intracranial pressure fluctuations. For this reason, improvements concerning the handling and the construction of the extractor have been repeatedly proposed.
Thus, for example, from U.S. Pat. No. 2,702,038 (FIG. 6) a vacuum extractor is known where a rigid handle is connected with the vessel via a ball joint to permit better positioning and directing of the vacuum extractor. Such a ball joint, however, does not permit, under traction, a frictionless swiveling of the rigid handle or a free rotation of the head, as a power coupling will occur in the joint. This in turn is what makes the bringing out of the infant's head from the birth canal much more difficult.
Also a vacuum extractor is known in which the force is measured with which the scalp presses against a contact plate disposed in the interior of the vessel during evacuation of the vessel. By the measurement of this pressing force, however, a possible state of danger, in which detachment of the vessel takes place, is not sufficiently predictable, because the pressing force of the scalp is being varied in an entirely unpredictable manner depending on traction forces acting on the vessel from different directions.
The arrangement known from German Patent DE-PS No. 31 38 589 (in which harmful pressure fluctuations upon detachment of the vessel are to be reduced by the fact that a tissue holding device disposed in the interior of the vessel delays a swinging back of the scalp is disadvantageous because with a vessel of such a nature only relatively small traction forces can be transmitted.
It may be said in general that with all known vacuum extractors there is a problem in the sense that the vacuum built up in the vessel collapses abruptly upon exertion of tensile forces (in particular tensile forces not directed coaxially) when in the edge region of the vessel opening a connection is established between the evacuated region and the surrounding. Besides the calculable maximally applicable traction force (which depends on the diameter of the evacuated vessel), such parameters as in particular the direction of pull, the tilting moment and the tissue properties of the head swelling play a decisive role, so that in the final analysis traction and pressure measurements alone cannot indicate reliably enough a threatening detachment, unless in the evaluation of the measurement results a safety zone is taken into account. Taking such a safety zone into consideration, however, would lead to a definite limitation of the employable traction forces.